Born in Camberwell, an inner eastern suburb of Melbourne, Trask learned to sing at an early age, performing at school functions and for her family. At the age of 16, she became a part of a singing group and she soon opened for top stars, including Frank Sinatra and Sammy Davis Jr., who were touring Australia - Sinatra and Davis wanted Trask to move to America to further her solo career there. She became a regular on Don McNeill's Breakfast Club TV show and appeared as a dancer and singer on the Jack Benny TV show. She was soon noticed by the conductor Mitch Miller, who in 1960 decided to give her a recording contract with Columbia Records and also make her a regular on his show Sing Along with Mitch. Trask released two albums in 1961 and 1962 geared towards the pop market but neither were successful. After Miller's show was cancelled in 1964, Trask and her new husband, Thom McEwen, decided to move back to Australia so that she could restart her career there.
In 1967, Trask and her husband moved back to the United States and settled in Nashville so that she could become a country singer. She signed with Dial Records that year, and in early 1968 had her first country chart single with "Lock, Stock, and Teardrops", which was a minor hit only reaching the top 70. It was enough to garner her a major record deal with Dot Records that same year and she released an album which would become her nickname "Miss Country Soul", later released in the UK on Ember Records. The album featured versions of R & B hits such as "Hold on To What You Got", "Show Me", and also displayed her soulful voice as well. The album drew critical acclaim but the single released "Hold on To What You Got" only reached the top 60. It was not until 1970 when Diana first reached the Top 40 on the country charts with her version of Patsy Cline's "I Fall to Pieces" and "Beneath Still Waters" (a decade later a Number 1 hit for Emmylou Harris). Starting in 1972, Trask had a string of major hits with songs including "We've Got To Work It Out Between Us" (1972), "It Meant Nothing To Me" (1972), and 4 straight Top 20 hits with "Say When" (1973), "It's A Man's World (When You Have A Man Like Mine)" (1973), "When I Get My Hands on You" (1974), and "Lean It All on Me" (1974), which latter song would become her biggest hit, reaching number 13 on the country charts and a minor pop hit as well nearly breaking into the Top 100. This track was also issued as a single in the UK, backed with 'Behind Closed Doors' where Ember Records issued many of Diana's Dot recordings. She also toured the UK with Glen Campbell who wrote the sleeve notes for her most successful Ember album.
Later career and present
Trask continued with Dot Records with two more hits, "If You Wanna Hold On (Hold on to Your Man)" (1974) and "Oh Boy" (1975). These would become her last major hits. She continued releasing albums and singles with the label until 1977. She made a brief comeback on the Kari label in 1981 with two minor hits, "This Must Be My Ship" and "Stirrin' Up Feelin's". After this, she and her husband moved back to Australia, where she resumed her career. Trask wrote the song "I Think About Your Lovin'" which was a hit for The Osmonds in 1982.